In a cellular radio communications system, mobile terminals operate by radio communication with base stations of a mobile network. The terminal is typically camped to one base station, herein referred to as a serving base station. When the terminal moves within the coverage area of the network, or if the radio characteristics of the connection deteriorate, handover to another base station will sometimes be required. The principle idle mode cell selection in many cellular standards, e.g. the 3GPP standards for WCDMA and LTE, are based on mobile device detection of base station signals. Each device will experience the received signals differently, e.g. due different positions in a cell, and based on the experienced signal quality it may select a suitable cell for camping. The serving base station may store, or otherwise have access to, a neighbour cell list. This represents a list of at least the most nearby cell base stations, and may be transmitted from the serving base station to the mobile device. In order to prepare for handover, terminals are normally configured to perform measurements on at least neighbouring base stations, so as to determine its quality as a candidate cell for handover.
When a mobile terminal, also commonly referred to as user equipment UE, is in so-called idle mode, it is registered to a certain mobile network and camped to a base station. However, it is not active in any voice or data transmissions. In this mode, the terminal is typically configured to periodically listen to regularly broadcast information from the base station, in order to receive indication whether e.g. the terminal is being paged, e.g. due to an incoming phone call. The periodicity of this broadcast information determined by the network, and denoted idle mode Discontinuous reception (DRX) cycle. During these paging occasions the terminal will also utilize a received pilot signal from at least the serving base station, to determine the current radio conditions, such as signal strength and quality. As of today in 3GPP LTE standard, the DRX cycle can be between 0.32 s to 2.56 s.
In case the signal strength/quality is below a threshold when the terminal is in idle mode, the terminal may initiate additional measurements to find other potential base stations within proximity. Normally, measurements are made on pilot signals of neighbour cells, as given by the serving base station. If one or more such other base station pilot signals are received, the measured signal strength and quality from these base stations are compared to each other to determine if the terminal should make a cell reselection and thereby switch to continue being registered to a mobile network but being camped to another base station. The need for such cell reselection is typically occasioned by terminal mobility, when the terminal moves between the coverage areas of different base stations; i.e. between cells.
For the specific example of 3GPP, the frequency of such signal strength measurements of the serving cell is defined in TS 36.133, section 4.2.2.1. It is stated that “The UE shall measure the RSRP [Reference Signal Received Power] and RSRQ [Reference Signal Received Quality] level of the serving cell and evaluate the cell selection criterion S defined in [TS 36.304] for the serving cell at least every DRX cycle”. Within 3GPP there is work ongoing to define solutions for M2M type terminals, where one focus area is to reach very long battery lifetime. One proposed area to consider for standardization within 3GPP Release 13 timeframe is extended DRX cycles way beyond existing range, e.g. at least in the order of 10-60 seconds.
Extended DRX cycle will have implications on the base station control over measurement intervals, since measurements every DRX cycle will be relatively infrequent.
US2014295820 is related to this context, and discloses a method of controlling DRX operation of a signal for a terminal in a wireless communication system, which includes the steps of: measuring velocity-related information of the terminal; transmitting the measured velocity-related information to a base station; receiving from the base station, in response to the transmission of the velocity-related information, discontinuous reception operation set information for a variable discontinuous reception operation; and performing the discontinuous reception operation according to the received discontinuous reception operation set information.